The present invention relates to a heating, ventilation and air conditioning (HVAC) system for a vehicle cab.
Operator stations or cabs of most agricultural vehicles are surrounded by large areas of glass so that the operator can see the area being worked or the product being produced or harvested. These large glass surface areas transmit a lot of light and result in a significant solar heat load being applied through the glass surfaces into the cab. The large glass area can result in solar loading of a vehicle cabin similar to a mid-size home load with significantly greater floor square footage.
This solar heat load must be overcome by the air conditioning system in order to provide an acceptable level of comfort to the operator, and this is usually accomplished via spot cooling of the operator only, rather than cooling the entire space. Most vehicle air conditioning systems in use today have large heat rejection capacities in order to handle the large solar heat loads combined with heat loads from the vehicle engine and drive train, over which the cab is placed.
Because of the vehicle must operate in a dirty, debris-laden air, this large heat rejection capacity requires a large spacing between the fins of the heat exchanger cores to prevent them from being clogged with airborne debris, and this results in a rather large HVAC system. It is difficult to fit such large HVAC system into a vehicle or cab, and if a large enough system cannot be accommodated, then the cab designer may be forced to use a smaller HVAC system which may only be large enough to spot cool the operator. However, spot cooling is undesirable because it can result in over-cooling of portions of an operator's body, while insufficiently cooling anyone else who is in the operator's compartment.
To minimize the packaging impact to the performance to the vehicle or operator, traditionally, long thin heat exchanger cores have been used. However, these long, thin cores make heat transfer to the air flowing through them difficult to uniformly transfer heat between the air and the entire face area of the core due to the poor aspect ratio of the core faces to the fans used to push or pull air through the cores. This air-side heat transfer inefficiency resulted in core with even larger theoretical capacities and thus space requirements in order to obtain the required capacities increase even further.